1. Field of the Invention
The present invention relates generally to routing and forwarding solutions. More particularly, the present invention relates to a hybrid routing and forwarding solution for mobile or fixed wireless sensor networks.
2. Description of Related Art
A wireless sensor network (WSN) is a self-organizing wireless network that consists of distributed devices with sensors commonly referred to as “nodes”. The sensors are application specific. They are used for monitoring environmental conditions, such as sound, temperature, vibration, pressure, motion or pollutants at different locations. The wireless sensor network was originally motivated by military applications. It is now widely used in many industrial, agricultural, medical and other civilian applications.
In addition to the sensors, each device in a WSN is equipped with elements such as a radio transceiver, microcontroller, flash memory, antenna, energy source and so on. A WSN device is typically low data rate, low cost and low power devices. The low cost of a WSN is a constraint on system resources such as energy, memory, processor and bandwidth.
There are usually three types of WSN devices, i.e. the coordinator (or sink), router and end device. The first two devices have routing functionality. Both devices have ability to find proper routes to forward packets to desired destinations. An end device has no routing ability, it only communicates with a specific router that is called the parent of the end device.
If the routing condition changes so that the original path becomes unavailable, the routers are able to find a new path to deliver the packets to the destination. Currently, the WSN devices are usually installed in fixed locations. However, if the devices were installed inside a moving target, the routing among the wireless nodes becomes a challenge.
The routing protocols and forwarding processes are the major resource consumers of the software in a WSN. These modules require a good deal of memory, CPU time and a power resource. The wireless sensor nodes on the other hand, are typically low data rate, low cost and low power devices. Therefore, it is a challenge to provide routing and forwarding functionality in a WSN. Furthermore, it is an even bigger challenge in a mobile WSN since the physical locations of the nodes are changed dynamically. The mobile WSN creates significant amount of variables and requires extra resources and mechanisms.
Currently, there are many ways to implement routing and forwarding functionality in a mesh WSN. Most of them are data centric protocols because an address centric (with unicast shortest path) approach is commonly thought to take much more system resources and electric power. The data centric protocols usually are coordinator centric. They ignore the roles of the individual nodes. Yet the forwarding path is less deterministic. Below are typical examples of existing approaches. The first three are basically data centric, however the flooding mechanism works in an address centric way as well:
1. Flooding the data over the WSN. This approach is simple but it can create implosion problems. The same copies are flooded over the area until they reach the destination.
2. Sensor Protocols for Information via Negotiation (SPIN). This protocol forwards the data via negotiation that consumes less power than flooding, but the SPIN is not reliable, it cannot guarantee the delivery of the data.
3. Gossiping. At every step each node forwards data only to one neighbor which is selected randomly. The neighbor must then forward the data back to the sender. The Gossiping avoids flooding but is inefficient.
4. AODV (Ad-hoc On-demand Distance Vector) based routing protocol. This protocol uses route discovery and selection mechanisms. Its router request and route reply process is effective, but not economical.
5. Conventional address centric shortest path routing. This approach finds the shortest path and eliminates the flooding completely but requires constant routing advertisement that is expensive and consumes a good deal of resources and electric power.
6. Typical solutions for mobile WSN: mobile base station based solutions, mobile data collector based solutions, and rendezvous based solutions. The restriction for these existing solutions is that all the nodes must be fixed except a coordinator node.
Therefore, what is needed is a method of routing and forwarding that may efficiently allow intelligent and dynamic routing while eliminating waste. Moreover, the solution should allow for a mobile wireless sensor network.